General Mechanic welded cracks around the mounting bracket of the No. 3 bin vibrator in Bldg 400. To access the vibrator he pulled himself up between 2 pipes. As he did he felt a pull in his left shoulder. He was seen by the company doctor 12/7/2005 & given a restriction from overhead work, climbing and will be seen by a physical therapist. Not reported until 12/06/2005.